RICHMOND — The Virginia House on Wednesday approved a watered-down bill requiring women to undergo ultrasound imaging prior to having an abortion, removing a mandate for a more invasive procedure at the request of Gov. Bob McDonnell.

Since most abortions take place early in a pregnancy, the original bill, proposed in the House by Delegate Kathy J. Byron, Campbell Republican, would have required many women to undergo a transvaginal procedure to determine the gestational age of their child.

Delegate David B. Albo, Fairfax Republican, offered a substitute bill at the request of Mr. McDonnell that would give the woman the option of undergoing that procedure if one is deemed necessary. It would still, however, require women to undergo a transabdominal “jelly-on-the-belly” ultrasound.

Ms. Byron defended the substitute as still being anti-abortion.

“Some of the misinformation that has been circulating and the things I have learned over the last couple of weeks leads me to believe that informed consent is even more important,” she said.

State Sen. Jill Holtzman Vogel, Fauquier Republican, said that she intended to strike the version of the bill she introduced.when the substitute bill crosses back over to the Senate.

Mr. McDonnell, a Republican, had indicated support for the original legislation but on Wednesday issued a lengthy statement that said he maintains his anti-abortion stance and supports the informed-consent statute the bill would amend, but Virginia should not force women to undergo an invasive procedure without their consent.

Democrats blasted the substitute because it still mandates the less-invasive ultrasound. And they said it was rushed through the chamber without proper vetting.

“Where else can an individual, without the consent of the woman, apply petroleum jelly to her abdomen, run an instrument across it and not be charged with trespass, assault, sexual battery or aggravated sexual battery?” asked Delegate Joseph D. Morrissey, Henrico Democrat. “I cannot think of one.”

The issue attracted national attention in the past week, with comedian Jon Stewart lampooning it Tuesday night on Comedy Central’s “The Daily Show.” “Saturday Night Live” poked fun at both the ultrasound bill and a separate “personhood” measure that would define life as beginning at conception.

A handful of Democratic legislators have also appeared on national cable news shows to speak out against the legislation, and activists delivered more than 30,000 petitions opposing the two bills to Mr. McDonnell’s office Wednesday morning. A gathering of about 1,000 people opposing the measures took place on Capitol Square on Monday, with others around the state planned for Thursday.

The proposal placed Mr. McDonnell — a strong social conservative who campaigned and governed with a focus on jobs — in a tricky political position. Signing the original bill could have resulted in a backlash against state and national Republicans, considering the kind of attention it has received.

The national political image of Mr. McDonnell as a rising GOP star who has been an active surrogate for Mitt Romney’s presidential campaign was also at stake.

“As people began to look at that bill and began to see the implications of that bill, women and men all over the commonwealth and all over the country started to weigh in,” said House Minority Leader David J. Toscano, Albemarle Democrat. “And a governor who has his eye on the vice presidency began to say, ‘Wait a minute here; this is a problem.’ “

Democrats were not the only ones to criticize the proposed changes.

Delegate Robert G. Marshall, Prince William Republican and sponsor of the personhood measure, decried members of his own caucus, saying they were “sounding the call of retreat” on the ultrasound bill. He abstained from voting on the bill, which passed 65-32. The conservative Family Foundation sent out an email saying they were “very disappointed” with the outcome.

Senate Caucus Chairman A. Donald McEachin, Henrico Democrat, said the party does not intend to use the issue as leverage in negotiations over the proposed two-year, $85 billion budget.

“Both Democratic caucuses understand that this is about people, not about power,” he said. “We want this bill gone — there is no version of this bill that we will accept.”